In level sensors operating based on FMCW or pulse transit time procedures, electromagnetic or acoustic waves are emitted in the direction of a surface. The sensor then records the echo signals reflected by the filler and components inside the container, and derives the respective level from that. Other level sensors work according to the principle of guided microwaves.
The method normally used according to the current state of the art essentially builds upon a false echo storage process to be performed by the user when the container is empty.
DE 33 37 690 A1, U.S. Pat. No. 5,157,639 and EP 1 628 119 A2 describe such methods.
The methods described therein may lead to problems during practical implementation.